Stem cell-based immunomodulatory strategies are a new therapeutic frontier in clinical allotransplantation (Frank, et. al., Lancet 363:1411 (2004)). It has been found, for example, that adult bone marrow-derived mesenchymal stem cells (BM-MSC) can inhibit T cell proliferation in response to mitogens and alloantigens in vitro (Le Blanc, et al., Scand. J. Immunol. 57:11 (2003); Rasmusson, et al., Exp. Cell Res. 305:33 (2005)). Because of its easy accessibility, skin is a particularly attractive potential source of therapeutically useful stem cells. However, identification of molecular markers for the isolation and expansion of pure dermal stem cells is a significant problem and the specific biological effects of these cells are largely unknown.
Recently, a novel human ATP-binding cassette (ABC) transporter, ABCB5 P-glycoprotein, was cloned and it has been suggested that this protein may serve as a marker for the isolation of a subpopulation of stem cells (Frank, et. al., J. Biol. Chem. 278:47156 (2003); Frank, et al., Cancer Res. 65:4320 (2005); U.S. Pat. No. 6,846,883).